In the timbering or roof support of mines, it is a common practice to provide mine prop which support head trees at the upper ends of the mine props. The head trees can constitute girders which are connected to the upper ends of the mine props by so-called cap shoes, also referred to as cap knees, bar shoes, jointing shoes and with other similar terminology. A cap, therefore, is a head tree or girder, also referred to as a bar, beam, runner, head block, roof bar, running bar or roof timber.
In the past, the caps have generally been girders with a structural shape profile, e.g. a I beam or an H beam, whose flanged surfaces are provided with recesses or with knoppy formations which can be engaged by the cap shoes.
Caps with knoppy I beam or H beam structural shapes are utilized in mines, for example, as timbering sets in mine galleries and as supports or bracing in long wall/gallery transitions as well as for additional bracing in arched galleries and the like. The mine props which can be used are generally hydraulic ram props or two-part friction props on whose prop ends the cap shoe can be affixed by welding.
The cap shoe which constitutes the starting point for the present invention is a drop-forged part constructed in accordance with German Industrial Standard DIN 21 561 with a massive base plate and four cylindrical rises at the corners of this base plate and which engage in recesses of the knoppy cap form-fittingly. This eliminates the possibility of shifting of the cap relative to the props.
To ensure sufficient stiffness, the prior art cap shoe must be formed as a massive heavy body, utilizing large amounts of material so that the cost of the cap shoe is high and the cap shoe may be difficult to assemble with the prop.